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Fuel pump relay
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Posted by Ari [Email] (#2847) [Profile/Gallery] (more from Ari) on Wed, 17 Oct 2007 09:55:52 Share Post by Email
In Reply to: voltage at my fuel pump is a volt short, BreckSaab, Tue, 16 Oct 2007 15:11:48
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Always look for a break where things are already broken - connectors and relay contacts.

You have dirty contacts on the fuel pump relay. Those contacts close each time you start the car, and the large in-rush current of the pump causes a small arc. Same thing when the car shuts off. This arc builds up some carbon, which is a resistance. So, the current the pump draws through the contacts causes a voltage drop. Now, because there is a voltage drop at the contacts, they get warm. When they warm up, the resistance increases - this causes more of a voltage drop - so you get even less at the pump over time.

This could be at any connection - resistances build up at connection points, not in the middle of wires. But the most common is the relay. Pull the relay out, and squirt the socket with some contact cleaner. While it is drying, pop the cover off the relay and look at the metal contacts (look like little metal discs on the end of copper arms that move). I'll bet the mating surfaces are chewed up. Clean them up with some fine sandpaper or an emery board - don't sand them down, just knock off the crud. If they're really chewed up, think about replacing the relay. Put a shine on the relay lugs with a few quick, light wipes of the sandpaper (don't take off the finish, just brighten them up) and stick the relay back in. I'll bet you'll see full power at the pump.

posted by 192.249....

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